docs: remove section on single: true from webpack integration

[satya164]

If the user has other loaders that modify the css in his pipeline this will break, e.g. - url() with url-loader etc. and this will be a production-only bug due to the file being processed by css-loader only in development.

[codecov]

Codecov Report

Merging #162 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #162   +/-   ##
=======================================
  Coverage   97.53%   97.53%           
=======================================
  Files          19       19           
  Lines         406      406           
  Branches       83       83           
=======================================
  Hits          396      396           
  Misses         10       10

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